Many autoimmune and chronic inflammatory diseases are related to immunoregulatory abnormalities. Diseases such as systemic lupus erythematosis, chronic rheumatoid arthritis, multiple sclerosis and psoriasis have in common the appearance of autoantibodies and self-reactive lymphocytes.
Multiple sclerosis is the most common neurological disease of young people. It is believed to cost more in medical care and lost income than any other neurological disease of young adults.
Multiple sclerosis affects the myelin sheaths of nerves. Myelin is an insulating material that coats most axons and allows rapid signal conduction over long distances by saltatory conduction. It is thought that antibodies and specialised cells of the immune system attack the myelin coating. This process leads to inflammation and scarring (sclerosis) which damages blood vessels in the area by the formation of a lesion known as a plaque. These plaques are characterised by being infiltrated by cells of the immune system. This results in demyelination with the consequential loss of the rapid signal conduction.
A possible method of treating these autoimmune and inflammatory diseases is by suppressing T-cell proliferation and modulating their activation.
The early stages of T-cell activation may be conceptually separated into pre-Ca2+ and post-Ca2+ events (Cahalan and Chandy 1997, Curr. Opin. Biotechnol. 8: 749). Following engagement of antigen with the T-cell antigen-receptor, activation of tyrosine kinases and the generation of inositol 1,4,5-triphosphate lead to the influx of Ca2+ and the rise of cytoplasmic Ca2+ concentration. The rise in Ca2+ activates the phosphatase calcineurin, which then dephosphorylates a cytoplasmically localized transcription factor (N-FAT) enabling it to accumulate in the nucleus and bind to a promoter element of the interleukin-2 gene. Along with parallel events involving the activation of protein kinase C and ras, gene transcription leads to lymphokine secretion and to lymphocyte proliferation. Some genes require long-lasting Ca2+ signals while others require only a transient rise of Ca2+. Furthermore, Ca2+ immobilisation of the T-cell at the site of antigen presentation helps to cement the interaction between T-cell and the antigen-presenting cell and thereby facilitate local signalling between the cells.
Ion channels underlie the Ca2+ signal of T-lymphocytes. Ca2+ ions move across the plasma membrane through a channel termed the store-operated Ca2+ channel or the calcium release-activated Ca2+ channel. Two distinct types of potassium channels indirectly determine the driving force of calcium entry. The first is the voltage-gated Kv1.3 channel (Cahalan 1985, J. Physiol. 385: 197; Grissmer 1990, Proc. Natl. Acad. Sci. USA 87: 9411; Verheugen 1995, J. Gen. Physiol. 105: 765; Aiyar 1996, J. Biol. Chem. 271: 31013; Cahalan and Chandy 1997, Curr. Opin. Biotechnol. 8: 749) and the second is the intermediate-conductance calcium-activated potassium channel, IKCa1 (Grissmer 1993, J. Gen. Physiol. 102: 601; Fanger 1999 J. Biol. Chem. 274: 5746; Rauer 1999, J. Biol. Chem. 274: 21885; VanDorpe 1998, J. Biol. Chem. 273: 21542; Joiner 1997, Proc. Natl. Acad. Sci. USA 94: 11013; Khanna 1999, J. Biol. Chem. 274: 14838; Lodgson 1997, J. Biol. Chem. 272: 32723; Ghanshani 1998, Genomics 51: 160). When these potassium channels open, the resulting efflux of K+ hyperpolarizes the membrane, which in turn accentuates the entry of Ca2+, which is absolutely required for downstream activation events (Cahalan and Chandy 1997, Curr. Opin. Biotechnol. 8: 749).
The predominant voltage-gated channel in human T-lymphocytes is encoded by Kv1.3, a Shaker-related gene. Kv1.3 has been characterised extensively at the molecular and physiological level and plays a vital role in controlling T-lymphocyte proliferation, mainly by maintaining the resting membrane potential of resting T-lymphocytes. Inhibition of this channel depolarises the cell membrane sufficiently to decrease the influx of Ca2+ and thereby prevents downstream activation events. Advantageously the homotetrameric Kv1.3 channel is almost exclusively located in T-lymphocytes.
Accordingly compounds which are selective Kv1.3 blockers are thus potential therapeutic agents as immunosuppressants for the prevention of graft rejection, and the treatment of autoimmune and inflammatory disorders. They could be used alone or in conjunction with other immunosuppressants, such as selective IKCa1 blockers or cyclosporin, in order to achieve synergism and/or to reduce toxicity, especially of cyclosporin.
U.S. Pat. No. 5,494,895 discloses the use of a thirty-nine amino acid peptide, scorpion peptide margatoxin, as a selective inhibitor and probe of Kv1.3 channels present in human lymphocytes, and also as an immunosuppressant. However the use of this compound is limited by its potent toxicity.
International Patent Application publication No.s WO 97/16438 and WO 091716437, and U.S. Pat. No. 6,051,590 describe the use of the triterpene, correolide and related compounds as immunosuppressants in the treatment of conditions in mammals affected or facilitated by Kv1.3 inhibition.
U.S. Pat. No. 6,077,680 describes DNA segments and proteins of derived from sea anemone species, more particularly ShK toxin from Stichodactyla helianthus. The ShK toxin was found to block Kv1.1, Kv1.3, Kv1.4 and Kv1.6, but a mutant ShK-K22DAP found to selectively block Kv1.3.
ShK toxin has recently been shown to both prevent and treat experimental autoimmune encephalomyelitis in Lewis rats, an animal model for human multiple sclerosis (Beeton 2001, et al., Proc. Natl. Acad. Sci. USA 98:13942), by selectively targeting T-cells chronically activated by the myelin antigen, MBP (myelin basic protein). The same study also Indicated that chronically activated encephalitogenic rat T-cells express a unique channel phenotype characterised by high expression of Kv1.3 channels (approximately 1500 per cell) and low numbers of IKCa1 channels (approximately 120 per cell). This channel phenotype is distinct from that seen in quiescent and acutely activated cells and may be a functionally relevant marker for chronically activated rat T lymphocytes.
Khellinone, a substituted benzofuran and natural product from certain plants, and 8-Methoxypsoralen (8-MOP), both commercially available products have been found to have blocking activity on the Kv1.3 channel.

Khellinone, 8-MOP and four dimeric variants thereof were described in a Poster (abstract. No. 1078) at a meeting of the American Physiological Society in Snowmass, Colo. (The Physiologist 42: A12 (1999)). The authors were testing whether linking two active units with a spacer improved activity. Some of the bivalent derivatives were said to be ineffective, and others were said to block the Kv1.3 channel, but lack therapeutic utility due to their extreme sensitivity to hydrolysis (very poor stability) and high lipophilicity (poor solubility in clinical conditions).